Jets Sizes

[Mr.Badwrench]

Hey guys working on my 81 XS1100S had some carb problems since I got it.Tune up time got valves set pulled carbs,tore them down they look like right part,the question is on the main the stamped with 110 on top and what I am reading says they should be 137.5? Different makes of jets? The K and l kits have 110 jets in it also got use some advise please. Thanks Mike

[motoman]

Hey guys working on my 81 XS1100S had some carb problems since I got it.Tune up time got valves set pulled carbs,tore them down they look like right part,the question is on the main the stamped with 110 on top and what I am reading says they should be 137.5? Different makes of jets? The K and l kits have 110 jets in it also got use some advise please. Thanks Mike

If your scoot is an 80-81 Special, the original 110main jets ARE stock for that model those two yrs. Sig. shows 81, so that would make it an 81SG.

FWIW, K&L copy jets, whether pilots or mains are NOT sized same as Genuime Mikunis and will result with impriper running issues.

137.5 mains apply to 78-79 carbs

With the limited info., my guess would be the carbs have the original main jets. They would be correct and since being vacuum slide actuated carbs, stock jetting works fine sea level up to and above 12,000ft.

[mack]

Jets

110"s in 1 &4 carbs and 120's in 2&3 carbs. Pilots are 42.5.

[DGXSER]

All of this is making the assumption you have the stock carbs on the bike. The two simplest ways to tell if you have the older or newer style carbs is if you have two Ts between the carbs (one upper and one lower) or one, and looking at the mixture screw on the engine side to see if the screw is hidden down in a tunnel or exposed on top. One T with hidden screw is the newer style that would be correct for your bike.

The newer style use the 110 main jets, the older style use the 137.5 main jets. Without restarting an old debate, if you have K&L jets your using, I would not throw them out or blame them for poor running issued. I use them in my carbs, bike runs fine.

[BA80]

If it has 110's in it it's a pretty good bet they are the later carbs.

[MPittma100]

Jets

If you already have the correct jetting in the carbs, there is no reason for them to be changed. Old jets work fine. Your 1981 Special has a model designation of 1981SH.

110 in 1&4 carbs and 120 in 2&3 carbs. Pilots are 42.5 are the correct jet sizes if you have the original carbs as was previously mentioned.

The emulsion tubes have specific locations as well.

[jetmechmarty]

110 in 1&4 carbs and 120 in 2&3 carbs. Pilots are 42.5 are the correct jet sizes if you have the original carbs as was previously mentioned.

If your bike is in fact a 1981 XS11 Special or XS1100SH, 110-120-120-110 was the recommendation in the Clymer manual. The bike would have come stock with main jets at 110 across all four IAW factory literature.

After messing with mine extensively, I am coming to believe the folks at Clymer knew what they were doing when they recommended 120 on 2 & 3.

Use only genuine Mikuni jets or all bets are off as to what size you need. Jets R Us is an easy place to get them. Just be sure to order the real deal.

[Mr.Badwrench]

Jet Size

Want to thank everyone for thier input,helped my alot. The carbs air ilde screw is down in a hole and has plastic floats,Ibleave the are right parts for the bike. Ready to finsh building them go riding. Thanks agine Mike

[motoman]

Want to thank everyone for thier input,helped my alot. The carbs air ilde screw is down in a hole and has plastic floats,Ibleave the are right parts for the bike. Ready to finsh building them go riding. Thanks agine Mike

Recessed idle mix screw makes them 80 and later carbies.
BTW, engine/manifold side= fuel adjustment.
intake/filter side= air adjustment.

[DGXSER]

Since your bike is an 81, look at the float bowls. The drain to be exact. See if the drain is a bolt that screws straight up from the bottom, or if there is a nipple down with a screw that comes in from the side. That is a tell tale difference between the 80 and 81 carbs. 81 had the nipple with the drain screws.

The early 80s models had a crossover feeding fuel to the pilot jets requiring a rubber plug over the pilot jet opening. Not that I think you have these, but good to be sure.